1. Field of the Invention
The present disclosure relates to a construction field, and more particularly, to a system for pre-stressing a member of a structure by pre-tendon method.
2. Description of the Background Art
A pre-stress refers to a method for pre-stressing a member in an opposite direction with respect to a direction of a bending moment and a shear stress generated at a member by an external force, in which a tendon to which a tensile force has been applied is settled in the member.
A method for applying pre-stress to the member of the structure such as a beam, a girder, etc. is largely classified into a pre-tendon method and a post-tendon method.
According to the pre-tendon method, a tendon is installed at a mold, pre-stressed, and then concrete is poured into the mold. And once the poured concrete is cured, the tendon is settled into the member. After the poured concrete is cured, the tendon is cut.
The pre-tendon method is convenient since no further process such as grouting is required. However, the pre-tendon method has a disadvantage that a process for bending and installing the tendon in the member is difficult.
According to the post-tendon method, a sheath is arranged in a mold with a certain shape, and then concrete is poured into the mold. After the poured concrete is cured, a tendon is inserted into the sheath and pre-stressed. At the same time, both end portions of the tendon is settled into both end portions of a member.
The post-tendon method has an advantage that the tendon can be easily bent by the sheath. However, the post-tendon method has a disadvantage that further process such as an additional grouting between the sheath and the tendon is required. Accordingly, the post-tendon method is more complicated.
The conventional pre-stress method has been applied to a member only in a vertical direction (length direction) of the member due to the following reasons.
Influence of stress generated from the member in a horizontal direction (width direction) is less than influence of stress generated from the member in a vertical direction. Furthermore, it is difficult to arrange the tendon in the member in both directions, horizontal and vertical directions.
In case of a beam having a width less than a length, it is sufficient to perform a pre-stress only in a vertical direction.
However, in case of a member such as a slap and a box girder having a length and a width that are almost equal to each other, influence of stress generated in a horizontal direction of the member is too large to be ignored. Accordingly, pre-stress is applied not only in a horizontal direction but also in a vertical direction for structural stability.
Consequently, it is required to develop techniques for applying pre-stress in both directions, a horizontal direction and a vertical direction.